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A preamp, short for preamplifier, is an electronic device that amplifies a low-level audio signal to a level that can be recorded or broadcast. It is often used to boost the signal from a microphone or a musical instrument.

An audio interface, on the other hand, is a device that connects various audio equipment, such as a computer, to other devices, like microphones, guitars, or speakers. It often includes preamps for the input signals, but also provides additional features like phantom power, direct monitoring, and various input and output options.

So, the main difference is that a preamp only amplifies signals, while an audio interface also provides connectivity and additional features.